Mariana mud volcanoes

Map of serpentinite mud volcanoes from the Mariana fore-arc.[1]

Mud volcanoes in the Mariana fore-arc are a hydrothermal geologic landform that erupt slurries of mud, water, and gas. There are at least 10 mud volcanoes in the Mariana fore-arc that are actively erupting,[1] including the recently studied Conical, Yinazao, Fantagisna (informally known as Celestial seamount), Asut Tesoro (formerly Big Blue), and South Chamorro serpentinite mud volcanoes.[1][2] These mud volcanoes erupt a unique serpentinite mud composition that is related to the geologic setting in which they have formed.[1][3][2] Serpentinite mud is the product of mantle metasomatism due to subduction zone metamorphism and slab dehydration.[1][3][2] As a result, the serpentinite mud that erupts from these mud volcanoes often contains pieces of mantle peridotite material that has not fully altered during the serpentinization process.[1][2][3][4] In addition to pieces of altered mantle material, pieces of subducted seamounts (including corals) have also been found within the serpentinite muds.[1] Serpentinite mud volcanoes in the Mariana fore-arc are often located above faults in the fore-arc crust. These faults act as conduits for the hydrated mantle material to ascend towards the surface.[1][3] The Mariana mud volcanoes provide a direct window into the process of mantle hydration that leads to the production of arc magmas and volcanic eruptions.[5]

## Contents

* 1 Geologic setting
* 2 Formation of serpentinite mud
* 2.1 Reactions
* 3 Pore fluid chemistry
* 4 References

## Geologic setting

A fore-arc lies between a volcanic arc and a trench, and is where no magma is being generated. Active igneous volcanism is occurring at the Mariana volcanic arc and the Marina fore-arc is located at the convergent margin between the Pacific and Philippine tectonic plates, where the Pacific plate is subducting beneath the Philippine plate.[1][6][7] The Mariana system is part of the combined Izu-Bonin-Mariana subduction system that extends from Japan to the north to Palau in the south.[6][7] Subduction began between 52-50 Ma during a period of tectonic plate reorganization in the western Pacific.[6][8][9][10] The Mariana arc contains two volcanic arcs, one being the active arc and the other a remnant arc, which is an inactive volcanic arc, located further from the subduction zone.[7][11] The remnant arc was left behind as the trench migrated westward ~6 Ma and from spreading of the back arc that formed the Mariana trough. This process resulted in the eastward migration of active volcanism, the formation of a new volcanic arc,[11] and the eastward bow of the Mariana arc.[7][11]

## Formation of serpentinite mud

As the Pacific plate sinks into the mantle, the pelagic sediments and hydrated basalts begin to dehydrate, which releases water and volatiles into the mantle beneath the Mariana arc.[1][2] This mixture of water and volatiles interacts with the mantle peridotite material beneath the overriding Philippine plate. The Mariana fore-arc peridotite has a harzburgite composition, thus it contains mostly olivine and orthopyroxene (enstatite).[1][12][13][14] The hydration of olivine (Mg2SiO4) and enstatite (MgSiO4) in the mantle results in the formation of Mg-rich serpentine (Mg3Si2O5(OH)4) and brucite (Mg(OH)2).[1][15][16] This process is known as serpentinization.[17][18] Serpentine is a mineral group, and includes the minerals antigorite, lizardite, and chrysotile, all of which share the same chemical composition but vary crystallographically.

### Reactions

Brucite Lizardite (green) and Chrysotile (white) Serpentine.

(Olivine reaction): 2Mg2SiO4 \+ 3H2O ←→ Mg3Si2O5(OH)4 \+ Mg(OH)2 [15]

(Enstatite reaction): 6MgSiO3 \+ 3H2O ←→ Mg3Si2O5(OH)4 \+ Mg3Si4O10(OH)2 [16]

Olivine (green mineral cluster) Enstatite (dark crystals in image)

(Olivine + Enstatite reaction): Mg2SiO4 \+ MgSiO3 \+ 2H2O ←→ Mg3Si2O5(OH)4 [16]

Schematic cross section of serpentinite mud volcanoes and how they source material from the subduction channel.[1]

## Pore fluid chemistry

Pore fluid from the serpentinite mud volcanoes is water that contains a significant amount of dissolved H2, CH4, C2H6 gases (volatiles).[1] Trends in the H2 and CH4 concentrations within the pore fluids indicate that H2 production is driven by the serpentinization process, followed by abiotic (Fischer-Tropsch Type) CH4 production.[1] Compared to seawater, the pore fluids from these serpentinite mud volcanoes have lower Cl, Ca, Mg, Sr, Li, and Si concentrations but higher pH, alkalinity, K, Na, Rb, Cs, and Ba content.[4] The mud volcanoes closest to the trench (i.e., Yinazoa and Fantangisna) have elevated concentrations of Ca and Sr and low concentrations of K, Na, Cl, SO4, and B in their pore fluid.[1] In contrast, the pore fluids of mud volcanoes furthest from the trench (i.e., Asut Tesoru, Conical, and South Chamorro) have high pH values (up to 12.4), depleted concentrations of Ca and Sr, and elevated concentrations of K, Na, Cl, SO4, and B.[1][4] The fluid chemistry of Yinazao and Fantangisna are controlled by shallow subduction processes like diagenesis and opal dehydration, whereas the fluid chemistry of the Asut Tesoru is controlled by deeper subduction processes like decarbonation and clay mineral decomposition.[1][19][20][21]

## References

1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 Fryer, P.; Wheat, C.G.; Williams, T.; Expedition 366 Scientists (2017-11-06) (in en). International Ocean Discovery Program Expedition 366 Preliminary Report. International Ocean Discovery Program Preliminary Report. International Ocean Discovery Program. doi:10.14379/iodp.pr.366.2017. http://publications.iodp.org/preliminary_report/366/.
2. ↑ 2.0 2.1 2.2 2.3 2.4 Fryer, P.; Wheat, C. G.; Mottl, M. J. (1999). <0103:mbmvif>2.3.co;2 "Mariana blueschist mud volcanism: Implications for conditions within the subduction zone". Geology 27 (2): 103. doi:10.1130/0091-7613(1999)027<0103:mbmvif>2.3.co;2. ISSN 0091-7613. Bibcode: 1999Geo....27..103F. http://dx.doi.org/10.1130/0091-7613(1999)027<0103:mbmvif>2.3.co;2.
3. ↑ 3.0 3.1 3.2 3.3 Fryer, P., ed (1990) (in en). Proceedings of the Ocean Drilling Program, 125 Initial Reports. 125. Ocean Drilling Program. doi:10.2973/odp.proc.ir.125.101.1990. http://www-odp.tamu.edu/publications/125_IR/125TOC.HTM.
4. ↑ 4.0 4.1 4.2 Kahl, Wolf-Achim; Jöns, Niels; Bach, Wolfgang; Klein, Frieder; Alt, Jeffrey C. (2015). "Ultramafic clasts from the South Chamorro serpentine mud volcano reveal a polyphase serpentinization history of the Mariana forearc mantle" (in en). Lithos 227: 1–20. doi:10.1016/j.lithos.2015.03.015. Bibcode: 2015Litho.227....1K. https://linkinghub.elsevier.com/retrieve/pii/S0024493715001073.
5. ↑ Tatsumi, Yoshiyuki. (1995). Subduction zone magmatism. Eggins, Steve.. Cambridge, Mass., USA: Blackwell Science. ISBN 0-86542-361-X. OCLC 31740360.
6. ↑ 6.0 6.1 6.2 Wu, Jonny; Suppe, John; Lu, Renqi; Kanda, Ravi (2016). "Philippine Sea and East Asian plate tectonics since 52 Ma constrained by new subducted slab reconstruction methods: PHILIPPINE SEA PLATE TECTONICS-SLABS" (in en). Journal of Geophysical Research: Solid Earth 121 (6): 4670–4741. doi:10.1002/2016JB012923.
7. ↑ 7.0 7.1 7.2 7.3 Shervais, John W.; Reagan, Mark; Haugen, Emily; Almeev, Renat R.; Pearce, Julian A.; Prytulak, Julie; Ryan, Jeffrey G.; Whattam, Scott A. et al. (2019). "Magmatic Response to Subduction Initiation: Part 1. Fore-arc Basalts of the Izu-Bonin Arc From IODP Expedition 352" (in en). Geochemistry, Geophysics, Geosystems 20 (1): 314–338. doi:10.1029/2018GC007731. ISSN 1525-2027. PMID 30853858. Bibcode: 2019GGG....20..314S.
8. ↑ Reagan, Mark K.; Heaton, Daniel E.; Schmitz, Mark D.; Pearce, Julian A.; Shervais, John W.; Koppers, Anthony A.P. (2019). "Forearc ages reveal extensive short-lived and rapid seafloor spreading following subduction initiation" (in en). Earth and Planetary Science Letters 506: 520–529. doi:10.1016/j.epsl.2018.11.020. Bibcode: 2019E&PSL.506..520R.
9. ↑ Ishizuka, Osamu; Hickey-Vargas, Rosemary; Arculus, Richard J.; Yogodzinski, Gene M.; Savov, Ivan P.; Kusano, Yuki; McCarthy, Anders; Brandl, Philipp A. et al. (2018). "Age of Izu–Bonin–Mariana arc basement" (in en). Earth and Planetary Science Letters 481: 80–90. doi:10.1016/j.epsl.2017.10.023. Bibcode: 2018E&PSL.481...80I.
10. ↑ Ishizuka, Osamu; Taylor, Rex N.; Yuasa, Makoto; Ohara, Yasuhiko (2011). "Making and breaking an island arc: A new perspective from the Oligocene Kyushu-Palau arc, Philippine Sea: OLIGOCENE KYUSHU-PALAU ARC" (in en). Geochemistry, Geophysics, Geosystems 12 (5): n/a. doi:10.1029/2010GC003440.
11. ↑ 11.0 11.1 11.2 Fryer, Patricia (1995), Taylor, Brian, ed., "Geology of the Mariana Trough" (in en), Backarc Basins (Boston, MA: Springer US): pp. 237–279, doi:10.1007/978-1-4615-1843-3_6, ISBN 978-1-4613-5747-6, http://link.springer.com/10.1007/978-1-4615-1843-3_6, retrieved 2020-11-05
12. ↑ Reagan, Mark K.; Ishizuka, Osamu; Stern, Robert J.; Kelley, Katherine A.; Ohara, Yasuhiko; Blichert-Toft, Janne; Bloomer, Sherman H.; Cash, Jennifer et al. (2010). "Fore-arc basalts and subduction initiation in the Izu-Bonin-Mariana system: FORE-ARC BASALTS AND SUBDUCTION INITIATION" (in en). Geochemistry, Geophysics, Geosystems 11 (3): n/a. doi:10.1029/2009GC002871.
13. ↑ Reagan, Mark K.; Pearce, Julian A.; Petronotis, Katerina; Almeev, Renat R.; Avery, Aaron J.; Carvallo, Claire; Chapman, Timothy; Christeson, Gail L. et al. (2017-08-18). "Subduction initiation and ophiolite crust: new insights from IODP drilling" (in en). International Geology Review 59 (11): 1439–1450. doi:10.1080/00206814.2016.1276482. ISSN 0020-6814. Bibcode: 2017IGRv...59.1439R. https://www.tandfonline.com/doi/full/10.1080/00206814.2016.1276482.
14. ↑ Bloomer, Sherman H.; Hawkins, James W. (1987). "Petrology and geochemistry of boninite series volcanic rocks from the Mariana trench" (in en). Contributions to Mineralogy and Petrology 97 (3): 361–377. doi:10.1007/BF00371999. ISSN 0010-7999. Bibcode: 1987CoMP...97..361B. http://link.springer.com/10.1007/BF00371999.
15. ↑ 15.0 15.1 Okamoto, Atsushi; Ogasawara, Yuichi; Ogawa, Yasumasa; Tsuchiya, Noriyoshi (2011). "Progress of hydration reactions in olivine–H2O and orthopyroxenite–H2O systems at 250°C and vapor-saturated pressure" (in en). Chemical Geology 289 (3–4): 245–255. doi:10.1016/j.chemgeo.2011.08.007. Bibcode: 2011ChGeo.289..245O. https://linkinghub.elsevier.com/retrieve/pii/S000925411100341X.
16. ↑ 16.0 16.1 16.2 Ogasawara, Yuichi; Okamoto, Atsushi; Hirano, Nobuo; Tsuchiya, Noriyoshi (2013). "Coupled reactions and silica diffusion during serpentinization" (in en). Geochimica et Cosmochimica Acta 119: 212–230. doi:10.1016/j.gca.2013.06.001. Bibcode: 2013GeCoA.119..212O. https://linkinghub.elsevier.com/retrieve/pii/S0016703713003311.
17. ↑ Moody, Judith B. (1976). "Serpentinization: a review" (in en). Lithos 9 (2): 125–138. doi:10.1016/0024-4937(76)90030-X. Bibcode: 1976Litho...9..125M. https://linkinghub.elsevier.com/retrieve/pii/002449377690030X.
18. ↑ Hyndman, Roy D; Peacock, Simon M (2003-07-25). "Serpentinization of the forearc mantle" (in en). Earth and Planetary Science Letters 212 (3): 417–432. doi:10.1016/S0012-821X(03)00263-2. ISSN 0012-821X. Bibcode: 2003E&PSL.212..417H. http://www.sciencedirect.com/science/article/pii/S0012821X03002632.
19. ↑ A. Haggerty, Janet (1991). "Evidence from fluid seeps atop serpentine seamounts in the Mariana forearc: Clues for emplacement of the seamounts and their relationship to forearc tectonics" (in en). Marine Geology 102 (1–4): 293–309. doi:10.1016/0025-3227(91)90013-T. Bibcode: 1991MGeol.102..293A. https://linkinghub.elsevier.com/retrieve/pii/002532279190013T.
20. ↑ Hulme, Samuel M.; Wheat, C. Geoffery; Fryer, Patricia; Mottl, Michael J. (2010). "Pore water chemistry of the Mariana serpentinite mud volcanoes: A window to the seismogenic zone: PORE WATER CHEMISTRY OF MARIANA MUD VOLCANOES" (in en). Geochemistry, Geophysics, Geosystems 11 (1): n/a. doi:10.1029/2009GC002674.
21. ↑ Mottl, Michael J.; Wheat, C. Geoffrey; Fryer, Patricia; Gharib, Jim; Martin, Jonathan B. (2004). "Chemistry of springs across the Mariana forearc shows progressive devolatilization of the subducting plate" (in en). Geochimica et Cosmochimica Acta 68 (23): 4915–4933. doi:10.1016/j.gca.2004.05.037. Bibcode: 2004GeCoA..68.4915M. https://linkinghub.elsevier.com/retrieve/pii/S0016703704004466.

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